RFID technology is for example used for communication between an RFID transponder and a reader, in particular an RFID reading device. For example magnetic coupling between an antenna of the RFID transponder and an antenna of the reader is established. Communication is performed for example by means of radio-frequency, RF, fields with a frequency in the order of MHz, for example at 13.56 MHz. ALM RFID transponders communicate to the reader by generating a transmission signal to modulate a reader antenna signal on a reader antenna.
In order to reduce space consumption, RFID transponders with very small dimensions and consequently very small antenna sizes are required. A drawback of such small transponder antennas is a reduction of a possible operating range due to a limited load modulation amplitude at the reader antenna. Consequently, a reduction of the antenna size is limited in existing transponders.
In some existing approaches, transmission from the RFID transponder to the reader may be active only during times corresponding to modulation periods in passive load modulation devices. Such approaches may suffer from a reduced load modulation amplitude. In other approaches, the transmission may be active also during times corresponding to non-modulation periods in passive load modulation devices to increase the load modulation amplitude. A drawback of such approaches may be that more than two amplitude levels of the reader antenna signal may be caused. Therefore, the reader may have difficulties to correctly demodulate the reader antenna signal, which may lead to an increased error rate in the communication.
Furthermore, in existing approaches, an absolute value of a change, in particular an amplitude change, of the reader antenna signal at the beginning of a transmission frame may be different from an absolute value of the amplitude change of the reader antenna signal caused by modulation during the transmission frame. This may lead to an increased error rate for detecting a start of a message or to a reduced success rate of transponder reply detection.